SAN JOSE -- Within a couple of years, researchers at the University of Southern California believe 3D printing techniques will be used to construct entire buildings in less than a day.

As outrageous as it sounds, such machines can already extrude concrete walls with internal reinforcement fast enough to complete the shell of a 2,000-sq. ft. house in under 20 hours.

The technology was demonstrated this week at the Inside 3D Printing Conference and Expo here.

The robotic extruding method, called Contour Crafting, is comparable to its smaller 3D desktop printer counterparts in that it takes its orders from CAD software, which stores and executes the architectural designs. The designs can be customized on a construction site even as work is underway.

The machines can also automatically embed all the conduits for electrical, plumbing and air-conditioning, as well as place electronic sensors to monitor the building's temperature and health over time.

Behrokh Khoshnevis, a professor of industrial and systems engineering at the USC's Viterbi School of Engineering, is leading the effort to perfect the Contour Crafting construction technology.

Khoshnevis said that he expects the technology will be commercially viable within two years.

Contour Crafting could help solve one of the largest problems facing the world today, a lack of decent housing for more than a billion people, Khoshnevis said.

Today, construction is slow, labor intensive, inefficient -- and the most hazardous job in the world, with 400,000 people injured 6,000 to 10,000 killed in construction accidents every year in the U.S. alone.

Behrokh Khoshnevis, a professor of industrial & systems engineering, at the University of Southern California, narrates a demonstration of 3D construction using Contour Crafting where a robotic arm excretes clay or concrete and a metal guide is used to form walls that include a corrugated internal structure for strength. Because the walls are hollow, they have excellent insulating properties. Using Contour Crafting the shell of a 2,000 sq. ft. house, including floors, ceiling and roof, can be built in less than 20 hours -- custom designed on site.

"It is wasteful and emission causing and corruption prone. And, the cost is always over budget," Khoshnevis said. "What we aspire to do is create neighborhoods that are dignified at a fraction of the cost, a fraction of the time and far more safety with beautiful architectural designs."

Structures not only can be constructed of concrete but also of hybrid materials. For example, the outer shell of a wall can be plaster with polymer or cement filler. Steel reinforcement in for form of coils can also be added to the mix.

An example of a non-traditionally shaped home created with Contour Crafting (source: ContourCrafting.org)

A Contour Crafting-machine, which is made up of a metal gantry frame, along with the robotic extruding system, weighs about 500 pounds. It comes in two pieces and can be quickly erected on a construction site, Khoshnevis said.

The gantry frames can be modified to climb structures, creating one story at a time until it reaches the top of a building. Then the robotic gantry could climb back down the sides of the building.

Each layer of concrete extruded by the machine is four inches thick and about six inches in height. Using special hardeners in the concrete, the material is hard enough to support the next layer by the time the machine circumnavigates the outside perimeter of a structure.

Because the materials are extruded through a nozzle, the walls of a building can take any form - thus the name "Contour Crafting."